Hot-wall reactor method for making multi-wall carbon nanotubes

ABSTRACT

A method for preparing multi-wall carbon nanotubes comprising atomizing a precursor solution comprising an aromatic hydrocarbon and a carrier gas. The mixture is then injected through an ultrasonic atomization system to form atomized precursor droplets. Then by injecting the atomized precursor droplets from the top of a vertical chemical vapor deposition reactor, the droplets can then react with a reaction gas in the reactor vessel to form a film that adsorbs to a growth surface in the reactor vessel. Layer by layer multi-wall carbon nanotubes are formed. This method is repeated to form layers of the multi-wall carbon nanotubes. The nanotubes formed have an outer diameter of 10 nm-51 nm and a length to diameter aspect ratio of 7200-13200.

CROSS-REFERNCE TO RELATED APPLICATIONS

The present application is a Continuation of U.S. application Ser. No.15/960,109, now allowed, having a filing date of Apr. 23, 2018 which isa Continuation of U.S. application Ser. No. 15/882,217, now U.S Pat. No.9,988,275, having a filing date of Jan. 29, 2018which is a Continuationof U.S. application Ser. No. 14/877,644, now U.S. Pat. No.9,878,912having a filing date of Oct, 7, 2015.

BACKGROUND OF THE INVENTION

Technical Field

The present invention relates to a method for synthesizing multi-wallcarbon nanotubes utilizing atomization in an injection vertical chemicalvapor deposition reactor.

Description of the Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentinvention.

In the last decade. extensive studies have been conducted on thesynthesis of carbon nanotubes (CNT). Different paths of formation andprecursors result in a variety of carbon nanomaterials of numerousshapes and sizes. See N. M. Mubarak, E. C. Abdullah, N. S. Jayakumar,and J. N. Sahu, “An overview on methods for the production of carbonnanotubes,” J. Ind. Eng. Chem., vol. 20, no. 4, pp. 1186-1197, July2014; and H. Golnabi, “Carbon nanotube research developments in terms ofpublished papers and patents, synthesis and production,” Sci. Iran.,vol. 19, no. 6, pp. 2012-2022, December 2012, each incorporated hereinby reference in their entirety.

By tuning reaction specifications, one can produce single wall ormulti-wall CNT. CNT can be produced in large quantity by three basicmethods: arc discharge, laser ablation and chemical vapor deposition(CVD) methods. See A. Shaikjee and N. J. Coville, “The role of thehydrocarbon source on the growth of carbon materials,” Carbon N. Y.,vol. 50, no. 10, pp. 3376-3398, August 2012, incorporated herein byreference in its entirety. Among these three, modifications of CVDreactors have led to flexible and economical methods and theseproperties make CVD reactors an exceptional choice for, not onlyresearch purposes, but also for commercial applications with large scalereactors. See M. Paradise and T. Goswami, “Carbon nanotubes—Productionand industrial applications,” Mater. Des., vol. 28, no. 5, pp.1477-1489, January 2007; P. M. Ajayan, “Nanotubes from Carbon,” Chem.Rev., vol. 99, no. 7, pp. 1787-1800, July 1999; and A. Mamalis, L. O.Vogtländer, and A. Markopoulos, “Nanotechnology and nanostructuredmaterials: trends in carbon nanotubes,” Precis. Eng., vol. 28, no. 1,pp. 16-30. January 2004, each incorporated herein by reference in theirentirety.

A typical CVD reactor consists of two main parts in a horizontalassembly: a preheating zone and a reaction zone. A feed precursor, insolution form, enters from the preheating zone along with reaction gasand after vaporization; carrier gas takes the vapors to reaction zone,where reaction occurs. See R. Andrews, D. Jacques, A. M. Rao, F.Derbyshire, D. Qian, X. Fan, E. C. Dickey. and J. Chen, “Continuousproduction of aligned carbon nanotubes: a step closer to commercialrealization,” Chem. Phys. Left., vol. 303, no. 5-6, pp. 467-474, April1999; Y. Cheol-jin, Lee; Jae-eun, “Mass synthesis method of high puritycarbon nanotubes vertically aligned over large-size substrate usingthermal chemical vapor deposition,” U.S. Pat. No. 6,350,488 B1, 2002; A.Cao, L. Ci, G. Wu, B. Wei, C. Xu, J. Liang, and D. Wu, “An effective wayto lower catalyst content in well-aligned carbon nanotube films,” CarbonN. Y., vol. 39, no. 1, pp. 152-155, January 2001; S. Huang,“Substrate-supported aligned carbon nanotube films,” U.S. Pat. No.7,799,163 B1, 2010; and R. Andrews, D. Jacques, D. Qian, and T. Rantell,“Multiwall Carbon Nanotubes: Synthesis and Application,” Acc. Chem.Res., vol. 35, no. 12, pp. 1008-1017, December 2002, each incorporatedherein by reference in their entirety. Otherwise solid precursor is putin a boat, which is placed in the preheating zone and after theprecursor is vaporized then the carrier gas takes it to the reactionzone. The reactor works as a batch reactor and normally is used forresearch purposes. See M. H. Rümmeli, A. Bachmatiuk, F. Börrnert, F.Schäffel, I. Ibrahim, K. Cendrowski, G. Simha-Martynkova, D. Plachá, E.Borowiak-Palen, G. Cuniberti, and B. Büchner, “Synthesis of carbonnanotubes with and without catalyst particles.,” Nanoscale Res. Lett,vol. 6, no. 1, p. 303, January 2011; A. M. Cassell, J. a. Raymakers, J.Kong, and H. Dai, “Large Scale CVD Synthesis of Single-Walled CarbonNanotubes,” J. Phys. Chem. B, vol. 103, no. 31, pp. 6484-6492, August1999; N. Lee and S. Kr, “Method of vertically aligning carbon nanotubeson substrates at low pressure using thermal chemical vapor depositionwith DC bias,” U.S. Pat. No. 6,673,392 B2, 2004: F. Danafar, a.Fakhru'l-Razi, M. A. M. Salleh, and D. R. A. Biak “Fluidized bedcatalytic chemical vapor deposition synthesis of carbon nanotubes—Areview,” Chem. Eng. J., vol. 155, no. 1-2 pp. 37-48, December 2009; andH. Hou, A. K. Schaper, F. Weller, and A. Greiner, “Carbon Nanotubes andSpheres Produced by Modified Ferrocene Pyrolysis,” no. 24, pp.3990-3994, 2002, each incorporated herein by reference in theirentirety.

For solid-gas interactions, a vertical CVD reactor is used. Solidprecursor is continuously fed from the upper region of the reactor,where, after preheating, it enters into the reaction zone. Carrier gasis introduced from bottom of the reactor to fluidize the solid precursorand the reaction gas provides a reduced environment to accelerate thereaction. CNT form in the reaction zone and due to its low density, thecarrier gas takes unreacted fluidized solid precursor out from the topof the reactor. However, there are features like bed height, pressuredrop, fluidization velocity, product purity, reaction time control thatmake this system difficult to handle and to operate. See D. Venegoni, P.Serp, R. Feurer, Y. Kihn, C. Vahlas, and P. Kalck, “Parametric study forthe growth of carbon nanotubes by catalytic chemical vapor deposition ina fluidized bed reactor,” Carbon N. Y., vol. 40, pp. 1799-1807, 2002; Q.Weizhong, L. Tang, W. Zhanwen, W. Fei, L. Zhifei, L. Guohua, and L.Yongdan, “Production of hydrogen and carbon nanotubes from methanedecomposition in a two-stage fluidized bed reactor,” Appl. Catal. AGen., vol. 260, no. 2, pp. 223-228, April 2004; Y. Yen, M. Huang, and F.Lin, “Synthesize carbon nanotubes by a novel method using chemical vapordeposition-fluidized bed reactor from solid-stated polymers,” Diam.Relat. Mater., vol. 17, no. 3, pp. 567-570, 2008; Q. Weizhong, W. Fei,W. Zhanwen, L. Tana, Y. Hao, L. Guohua, and X. Lan, “Production ofCarbon Nanotubes in a Packed Bed and a Fluidized Bed,” AIChE, vol. 49,no. 3, pp. 619-625, 2003; F. Wei, Q. Zhang, Qian, H. Yu, Y. Wang, G.Luo, G. Xu, and D. Wang, “The mass production of carbon nanotubes usinga nano-agglomerate fluidized bed reactor: A multiscale space—timeanalysis,” Powder Technol., vol. 183, pp. 10-20, 2008; Y. Hao, Z.Qunfeng, W. Fei, Q. Weizhong, and L. Guohua, “Agglomerated CNTssynthesized in a fluidized bed reactor: Agglomerate structure andformation mechanism,” Carbon N. Y., vol. 41, pp. 2855-2863, 2003; C.Hsieh, Y. Lin, W. Chen, and J. Wei, “Parameter setting on growth ofcarbon nanotubes over transition metal/alumina catalysts in a fluidizedbed reactor,” Powder Technol., vol. 192, no. 1, pp. 16-22, 2009; Y.Wang, F. Wei, G. Luo, H. Yu, and G. Gu, “The large-scale production ofcarbon nanotubes in a nano-agglomerate fluidized-bed reactor,” Chem.Phys. Lett., vol. 364, no. 5-6, pp. 568-572, October 2002, eachincorporated herein by reference in their entirety.

Injection vertical CVD (IVCVD) for a liquid feed system is a modifiedprocess that has not been reported previously for CNT synthesis. Theprecursor solution is injected from top into the reactor by a newtechnique, an “ultrasonic atomization system.” The ultrasonicatomization system increases the surface area of the precursor prior toentering the preheating zone. See A. H. Lefebvre, Atomization and Spraysp. 434, incorporated herein by reference in its entirety. Reaction gasalong with carrier gas take feed droplets into the reaction zone whereCNT forms. Exhaust gases leave from the bottom of the reactor. By usingthis technique the efficiency of the reactor is increased. Anotheradvantage of using IVCVD reactor is that it operates at low pressure asno fluidization velocity is required to be maintained. See Q. Zhang,M.-Q. Zhao, J.-Q. Huang, Y. Liu, Y. Wang, W.-Z. Qian, and F. Wei,“Vertically aligned carbon nanotube arrays grown on a lamellar catalystby fluidized bed catalytic chemical vapor deposition,” Carbon N. Y.,vol. 47, no. 11, pp. 2600-2610, September 2009, incorporated herein byreference in its entirety.

There are different types of atomizer nozzles that can be used combinedwith an ultrasonic generator, like: narrow spray, wide spray with orwithout extension, radial spray and extra-long atomizer nozzle. See“Ultrasonic Atomizer Spray Nozzle Technology.” Available from SonozapCorp of Farmingdale, N.Y., USA, incorporated herein by reference in itsentirety.

Aromatic solvents like benzene, toluene, xylene, and phenol are usuallyused as a carbon source for multi wall CNTs synthesis.Organometallocenes are often used as a catalyst. See N. Koprinarov, M.Konstantinova, T. Ruskov, and I. Spirov, “Ferromagnetic NanomaterialsObtained by Thermal Decomposition of Ferrocene in a Closed Chamber,”Phys. vol. 34, pp. 17-32, 2007, incorporated herein by reference in itsentirety. Ferrocene is non carcinogenic and is preferred for large scaleproduction of CNT over other organometalic compounds (such asnickelocene). See O. Smiljanic, B. L. Stansfield, J.-P. Dodelet, A.Serventi, and S. Désilets, “Gas-phase synthesis of SWNT by anatmospheric pressure plasma jet,” Chem. Phys. Left., vol. 356, no. 3-4,pp. 189-193, April 2002, incorporated herein by reference in itsentirety.

In view of the forgoing the object of the present disclosure is toprovide a method for preparing CNT using an ultrasonic atomizationsystem and a vertical chemical vapor deposition reactor.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect, the present disclosure relates to a methodfor preparing multi-wall carbon nanotubes, including (i) atomizing aprecursor solution comprising an aromatic hydrocarbon and a carrier gas,wherein the precursor solution is injected through an ultrasonicatomization system to form ultrasonic atomized precursor droplets, (ii)injecting the ultrasonic atomized precursor droplets from the top of avertical chemical vapor deposition reactor into a preheating zone, (iii)reacting a reaction gas with the ultrasonic atomized precursor dropletsin the vertical chemical vapor deposition reactor to form a filmprecursor that adsorbs to a growth surface in the vertical chemicalvapor deposition reactor to form a layer of multi-wall carbon nanotubes,and (iv) repeating the atomizing, the injecting of the ultrasonicatomized precursor molecule, and the reacting until one or more layersof the multi-wall carbon nanotubes are formed and then removing themulti-wall carbon nanotubes from the growth surface. The present methodproduces multi-wall carbon nanotubes which are characterized by an outerdiameter of 10 nm-51 nm, a length to diameter aspect ratio of7200-13200.

In one embodiment the method of the present disclosure provides a70%-95% yield based on a 6%-10% conversion rate of the precursorsolution.

In one embodiment the precursor solution further comprises anorganometallic catalyst.

In one embodiment the organometallic catalyst is an organometallocenecatalyst, and the organometallocene catalyst is present in an amountfrom 0.3-2.0 wt % relative to the total weight of the precursorsolution.

In one embodiment the carrier gas is an inert gas.

In one embodiment the inert gas is argon.

In one embodiment the ultrasonic atomizing system comprises anultrasonic generating unit and an atomizing nozzle.

In one embodiment the ultrasonic atomization system produces anultrasonic frequency of 15 kHz-25 kHz.

In one embodiment the atomizing nozzle has a 0.1-0.2 cm aperture andradial spray angle of 125°-140°.

In one embodiment the precursor solution is injected through theatomizing nozzle with a flow rate of 80-110 mL/min.

In one embodiment the vertical chemical vapor deposition reactor has atleast four sections: a preheating zone, a reaction zone, a cooling zoneand a collector.

In one embodiment the reacting takes place in the reaction zone, whichis heated by a furnace to a temperature of 750° C.-1100° C.

In one embodiment the atomizing comprises injecting the precursorsolution at 75-105 mL/hour through the ultrasonic atomization system.

In one embodiment the atomizing forms ultrasonic atomized precursordroplets with a diameter of 0.9 μm-500 μm.

In one embodiment the reaction gas is comprised of a 5:1-3:2 ratio ofreacting gas to carrier gas.

In one embodiment the reacting gas is a reducing gas.

In one embodiment the reducing gas is hydrogen gas.

In one embodiment, the reacting takes place in the reaction zone at apressure less than 1.5 bar and a temperature of 750° C.-1100° C.

In one embodiment the vertical chemical vapor deposition reactor is ahot-wall reactor.

In one embodiment the growth surface is comprised of quartz.

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is an exemplary schematic of an ultrasonic atomization systemwith an atomizing nozzle 101, nozzle stern 102, and an ultrasonicgenerating unit 103.

FIG. 2 is an exemplary schematic of an injection vertical chemical vapordeposition reactor.

FIG. 3 is an exemplary velocity profile 302 of the spray from anatomizer nozzle 301.

FIG. 4A is a scanning electron microscopy (SEM) image of multi walledmulti-wall carbon nanotube 200 μm scale.

FIG. 4B is a SEM image of multi walled multi-wall carbon nanotube 500 nmscale.

FIG. 5A is a transmission electron microscopy (TEM) image of a singlemulti-wall carbon nanotube shown with an arrow indicating its crosssection.

FIG. 5B is a TEM image of walls of multi-wall carbon nanotube arevisible.

FIG. 5C is a TEM image of multi-wall carbon nanotube with its catalystparticle indicated by an arrow.

FIG. 6A is an image if the region used for energy-dispersive X-Rayspectroscopy (EDS).

FIG. 6B is an EDS characterization for sampled area shown in FIG. 6A.

FIG. 6C is a table describing the EDS characterization in FIG. 6B, forsampled area shown in FIG. 6A.

FIG. 7A is a SEM image of a high aspect ratio multi-wall carbonnanotube.

FIG. 7B is a SEM image of a second view of a high aspect ratiomulti-wall carbon nanotube.

FIG. 7C is a SEM image of a large wafer of multi-wall carbon nanotube.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views.

According to a first aspect, the present disclosure relates to a methodfor preparing multi-wall carbon nanotubes, including atomizing aprecursor solution comprising an aromatic hydrocarbon and a carrier gasin a vertical chemical vapor deposition reactor. The aromatichydrocarbon can include, but is not limited to xylene, benzene, toluene,phenol, camphor and isomers thereof. Additionally, there can be mixturesof aromatic hydrocarbons to produce CNT. The carrier gas can include,but is not limited to argon, xenon, krypton, neon, or nitrogen. In oneembodiment, argon is the preferred carrier gas. The carrier gas isintended to be inert to the chemical reactions taking place inside thevertical chemical vapor deposition reactor. The ratio of the volume ofcarrier gas to the volume of aromatic hydrocarbon can be at least 50:1,at least 40:1, at least 30:1, at least 20:1, at least 10:1. FIG. 2depicts an exemplary reactor setup that includes an attachment for gascylinders 210 that contain the carrier gas and a mixing and a regulatorapparatus 211 that may be used to control the flow and volume ratio ofthe carrier and aromatic hydrocarbon gasses.

In one embodiment the precursor solution further comprises anorganometallic catalyst. In one embodiment the organometallic catalystis an organometallocene catalyst, and the organometallocene catalystforms at least 0.1 wt % of the total weight of the precursor solution,at least 0.5 wt % of the total weight of the precursor solution, atleast 0.75 wt % of the total weight of the precursor solution, at least1.0 wt % of the total weight of the precursor solution, at least 0.5 wt% of the total weight of the precursor solution, at least 1.5 wt % ofthe total weight of the precursor solution, at least 2.0 wt % of thetotal weight of the precursor solution, at least 2.5 wt % of the totalweight of the precursor solution, at least 3.0 wt % of the total weightof the precursor solution. Metallocenes are a type of sandwich compound,an organometallic complex featuring a metal bound by haptic covalentbonds to two arene ligands. A metallocene is a compound typicallyconsisting of two substituted or unsubstituted cyclopentadienyl anions(Cp, which is C₅H₅ ⁻) bound to a metal center (M) in the oxidation stateII or IV, with the resulting general formula (C₅H₅)₂M or (C₅H₅)₂MX₂,e.g., ferrocene, cobaltocene, and nickelocene. As referred to herein,the term “substituted” means that at least one hydrogen atom is replacedwith a non-hydrogen group, provided that normal valencies are maintainedand that the substitution results in a stable compound. Exemplary cpgroups include, but are not limited to cyclopentadienyl,pentamethylcyclopentadienyl, and 1,2-diphenyl cyclopentadienyl. Further,the metallocene catalyst may refer to several classification types,including but not limited to parallel, multi-decker, half-sandwich, bent(tilted), and multi-cyclopentadienyl complexes. In one embodiment,inclusion of the catalyst in the precursor solution results in thecatalyst becoming embedded within the multi-wall carbon nanotubeproduct, which may advantageously provide structural support to themulti-wall carbon nanotubes. In addition to organometallocene catalysts,other categories of organometallic catalysts can be used in the presentmethod, such as alkyl catalysts, aryl catalysts, phosphine catalysts,pthalocyanine catalysts and the like. The organometallic catalyst caninclude, but is not limited to iron pentacarbonyl, phenylsilver,chloro(cyclopentadienyl)bis(triphenylphosphine)mthenium,triethylaluminium, and nickel pthalocyanine.

The present method includes atomizing a precursor solution with theultrasonic atomization unit. The ultrasonic atomization unit is placeddirectly before the preheating zone of the reactor. To atomize theprecursor solution, the carrier gas is injected with the precursorsolution through an ultrasonic atomization system (FIG. 1) to formultrasonic atomized precursor droplets. In one embodiment, the precursorsolution is injected into the ultrasonic atomization system at a flowrate of at least 60 mL/hour, at least 70 mL/hour, at least 80 mL/hour,at least 90 mL/hour, at least 100 mL/hour, at least 110 mL/hour, atleast 120 mL/hour. As shown in FIG. 2, the precursor solution, held in areservoir 215, can be injected by various pumps 214 including, but notlimited to a diaphragm pump, a peristaltic pump, an impeller pump, ascrew pump, and a piston pump. The pumps size is configured to theappropriate size of the reactor. Similarly, the flow rate of thesolutions and gases can be increased for larger reactors. For example,doubling the size of the reactor would correspond to a doubling of theflow rate. FIG. 1 is a schematic of an exemplary ultrasonic atomizationsystem with an atomizing nozzle 101, nozzle stem 102, and an ultrasonicgenerating unit 103. The ultrasonic generating unit comprises amechanism to convert electrical energy into mechanical energy, oftenunderstood as the piezoelectric effect. In one embodiment the ultrasonicgenerating unit uses a piezoelectric crystal to generate ultrasonicwaves that result in frequencies that generate atomized droplets of asolution. In one embodiment, the ultrasonic atomization unit has anoperating frequency of at least 15 kHz, at least 20 kHz, at least 25kHz, at least 30 kHz, at least 35 kHz. The power output of theultrasonic atomization unit is at least 150 W, at least 100 W, at least75 W, at least 50 W, at least 25 W, at least 10 W. Once the precursorsolution is injected into the ultrasonic atomization system, thenear-ultrasonic or ultrasonic frequency atomizes the solution intodroplets with diameters of at least 0.5 μm, at least 1.0 μm, at least 10μm, at least 20 μm, at least 25 μm, at least 50 μm, at least 75 μm, atleast 100 μm, at least 200 μm, at least 300 μm, at least 400 μm, atleast 500 μm. The ultrasonic atomized precursor droplets flow throughthe atomizing nozzle at a rate of at least 60 mL/min, at least 70mL/min, at least 80 mL/min, at least 90 mL/min, at least 100 mL/min, atleast 110 mL/min, and at least 120 mL/min. FIG. 3 depicts a schematic ofthe velocity profile of the ultrasonic atomized precursor droplets 302as they are injected through the atomizing nozzle 101 into a preheatingzone 201 of the vertical chemical vapor deposition reactor and againstthe walls of the reactor 303. In one embodiment the atomizing nozzle hasat least a 0.05 cm diameter aperture, at least a 0.1 cm diameteraperture, at least a 0.15 cm diameter aperture, at least a 0.2 cmdiameter aperture. The nozzle of the atomizer may also have multipleapertures of various sizes and shapes to produce different dispersiveangles and variation in the velocity profile of the droplets as theyleave the atomizer nozzle. The wide range atomizer nozzle produceswidely dispersed droplets over a wider area than a narrow nozzle due tothe angle portion of the tip. In one embodiment, the radial spray angleof the nozzle is between 120°-160°, between 125°-155°, between130°-150°, between 135°-145°, between 135°-140°.

In one embodiment, the ultrasonic atomized precursor droplets areinjected through the atomizing nozzle 101 from the top of a verticalchemical vapor deposition (VCVD) system (FIG. 2). The vertical chemicalvapor deposition reactor has at least four sections: a preheating zone201, a reaction, zone 202, a cooling zone 203 and a collector 204.During the process of chemical vapor deposition the reaction zone isheated by a furnace to a temperature of at least 700° C., at least 750°C., at least 800° C., at least 850° C. at least 900° C., at least 950°C. at least 1000° C., at least 1050° C., at least 1100° C. In oneembodiment, the reaction zone 202 is held at a constant temperatureduring the reacting. A constant temperature refers to a temperature thatdoes not change by more than 5%, preferably 4%, preferably 3%,preferably 2%, more preferably 1%. During the reacting the reaction zoneof the reactor vessel is held at a pressure less than 5.0 bar, less than4.5 bar, less than 4.0 bar, less than 3.5 bar, less than 3.0 bar, lessthan 2.5 bar, less than 2.0 bar, less than 1.5 bar, and less than 1.0bar. In one embodiment the reactor vessel is a hot-wall reactor.

After the ultrasonic atomized precursor droplets are injected into thereactor vessel a reaction gas is injected to react with the ultrasonicatomized precursor droplets. The reacting gas is also a reducing gas,which reduces the chemical environment of the reactor vessel. In oneembodiment the reaction gas is comprised of preferably a 5:1 ratio ofreacting gas to carrier gas, preferably a 9:2 ratio of reacting gas tocarrier gas, preferably a 4:1 ratio of reacting gas to carrier gas,preferably a 7:2 ratio of reacting gas to carrier gas, preferably a 3:1ratio of reacting gas to carrier gas, preferably a 5:2 ratio of reactinggas to carrier gas, preferably a 2:1 ratio of reacting gas to carriergas. The reacting gas may include but is not limited to hydrogen gas,ammonia gas, hydrogen sulfide gas, or methane gas, but preferablyhydrogen gas. The reacting gas of the reaction gas and the ultrasonicatomized precursor droplets react to form a film precursor that adsorbsto a growth surface in the reactor vessel to form a layer of multi-wallcarbon nanotubes at least about 10 nm thick. at least about 7 nm thick,at least about 5 nm thick, at least about 2 nm thick, at least about 1nm thick. at least 0.75 nm thick, at least about 0.5 nm thick, at leastabout 0.25 nm thick, at least about 0.1 nm thick. The growth surface caninclude, but is not limited to the wall of the reactor vessel in thecollecting zone 204 of the reactor vessel or a specific surface placedin the collecting zone of the reactor vessel. The composition of thegrowth surface can include, but is not limited to quartz, zeolite,silicon, germanium, aluminum oxide, and silicon carbide.

Repetitively and/or continuously atomizing the precursor solution,injecting the ultrasonic atomized precursor droplet and reacting withthe reaction gas results in multi-wall carbon nanotubes (MWCNT) formedon the growth surface in the reactor vessel. In one embodiment, thepresent method produces MWCNT which are characterized by an outerdiameter of at least approximately 1 nm up to approximately 100 nm, atleast approximately 10 nm up to 90 nm, at least approximately 20 nm upto 80 nm, at least approximately 30 nm up to 90 nm, at leastapproximately 40 nm up to 60 nm. Furthermore, the MWCNT produced have alength to diameter aspect ratio of at least approximately 7000 up toapproximately 13500, at least a length to diameter aspect ratio ofapproximately 7500 up to approximately 13000, at least a length todiameter aspect ratio of approximately 8000 up to approximately 12500,at least a length to diameter aspect ratio of approximately 8500 up toapproximately 12000, at least a length to diameter aspect ratio ofapproximately 9000 up to approximately 11500, at least a length todiameter aspect ratio of approximately 9500 up to approximately 11000,at least a length to diameter aspect ratio of approximately 10000 up toapproximately 10500. The method of the present disclosure can provide atleast a 60% up to a 98% yield, at least a 65% up to a 95% yield, atleast a 70% up to a 90% yield, and at least a 75% up to a 85% yieldbased on at least a 1% to at least a 15% conversion rate of theprecursor solution, at least a 3% to at least a 12% conversion rate ofthe precursor solution, at least a 5% to at least a 10% conversion rateof the precursor solution.

The MWCNT formed by this method may be in various structures such asparchment, Russian doll, and in layers. In the parchment form the MWCNTwraps around itself like a parchment, such that a view of its crosssection would appear as a spiral. In the Russian doll structure, themulti-wall CNT forms as concentric cylinders of nanotubes. In rare casesthe CNT may form into flat layers that can stack upon each other formingaligned wafers (FIG. 7C). CNT yield obtained by this method can be atleast 75% aligned wafers, at least 65% aligned wafers, at least 55%aligned wafers, at least 45% aligned wafers, at least 35% alignedwafers, at least 25% aligned wafers, at least 15% aligned wafers, atleast 5% aligned wafers.

FIG. 5C shows a particle of ferrocene catalyst embedded in the center ofa MWCNT. In one embodiment, the embedded catalyst provides a support tothe growing MWCNT during the CVD process by increasing the tensilestrength of the MWCNT. The tensile strength can be increased by as muchas 20%, by as much as 15%, by as much as 10%, by as much as 5%, by asmuch as 2.5%, by as much as 1%. The various structural formations of CNTcan also be directed by the embedded catalyst due to electronicinteraction from the metal center of the catalyst with the carbon at thesurface of the MWCNT. Additional functionalization is also possible dueto the embedded catalysts.

The examples below are intended to further illustrate protocols forpreparing multi-wall carbon nanotubes synthesis using the atomizationsystem, in chemical vapor deposition.

EXAMPLE 1

Experimental Method

Materials

pXylene (96-99%) was purchased from Sigma-Aldrich Co. LLC. and was usedwithout further purification. Ferrocene was purchased from HoneywellRiedel-de Haen International Inc. with 96-99% purity and was usedwithout further purification. Ultrasonic atomization system was boughtfrom Sonaer Inc. which has two parts: (i) ultrasonic generator which canproduce frequency up to 20 kHz and (ii) wide spray atomizer nozzle thatallows up to 100 ml/min fluid flow (FIG. 1).

Catalytic solution and the precursor were injected into the reactorusing wide range ultrasonic atomizer nozzle fitted in the IVCVD reactorhead. CNT diameter and aspect ratio is controlled by reactiontemperature. See Q. Zhang, J.-Q. Huang, M.-Q. Zhao, W.-Z. Qian, and F.Wei, “Carbon nanotube mass production: principles and processes.,”ChemSusChem, vol. 4, no. 7, pp. 864-89, July 2011, incorporated hereinby reference in its entirety. By changing and repeating various reactionconditions advantageous reaction temperature was found to be 850° C.SEM, TEM and EDS were used to characterize the synthesize MWCNT.

Procedure:

The quartz wall vertical reactor and setup used for CNT synthesis isshown in FIG. 2. It has four main parts; preheating zone, reaction zone,cooling zone and collector. Feed solution enters from top of the reactorand passed through preheating zone to reaction zone, where (aftervarious reactions) 90% of yield was observed. Cooling zone helps to cooldown reactor temperature after completion of reaction. CNT is scrappedfrom quartz wall of the reactor and is collected from the collector.

The reactor was heated by an electric furnace until temperature reachedto 850° C. and was held constant at this temperature. Argon (Ar) waspurged into the reactor, from top, to remove any undesirable gas and wascontinuously injected to control the reaction time of CNT. pX was usedas carbon source and FCN; as Fe source; for CNT synthesis. One weightpercent catalytic solution (CS) of FCN in pX was prepared and injectedinto the atomizer nozzle via syringe pump at the flow rate of 90 ml/hrfor half hour.

Ultrasonic atomization system was installed at the head of reactor whichwas operated at high frequency, 20 kHz, to obtain smallest droplet size.Atomizer nozzle was placed in a way that its leg; which is 2.18 cm,appeared in the quartz region of the reactor. CS passed through atomizernozzle and spread in the reactor in an umbrella-shape profile (FIG. 3).This injection system increased the surface area of CS and made evenlydistribution of CS particles. When the atomization of CS was observed inthe quartz reactor, H₂; which acted like reaction gas (RG), was alsoinjected from top of the reactor along with Ar in the ratio of 3:1respectively.

Reaction took place in the reaction zone of the reactor and CNTdeposition on the quartz wall was observed. Electric furnace was turnedoff after completion of reaction. RG was stopped and system was cooledin Argon atmosphere. CNT was scrapped from quarts walls of the reactorand was collected from collector.

Results and Discussion

Multi-wall carbon nanotubes were synthesized and characterized by usingSEM, HRTEM, and EDS. After series of experiments optimum condition ofmaximum yield was found for proposed injected vertical chemical vapordeposition (IVCVD) reactor fitted with ultrasonic atomizing head system.The injected vertical CVD reactor has not been reported before andultrasonic atomization system has also not been used previously for CNTsynthesis. Feed stream and reaction gas direction is selected from topof IVCVD reactor in concurrent flow so that reaction time can beincreased and to sweep synthesize CNT. Ar was used.

The synthesized MWCNT were collected from collector of the reactor and7.43% conversion of catalytic solution was found. By using ultrasonicatomizer, the size of catalytic solution decreased to microns prior toentering into the pre-heating zone of the reactor. This scheme enhancedthe surface area of catalytic solution resulting into high yield thathas not been reported previously. The MWCNT synthesis efficiency wasincreased with the combination of IVCVD reactor and the ultrasonicatomizer.

SEM images of a sample showed vertically aligned MWCNT (FIG. 4A) andfurther investigation of the sample showed the CNT were straight andseparated from each other (FIG. 4B). This behavior indicates that CNThave high surface area.

Transmission electron microscope was used to investigate the placementof catalyst, structure of CNT and shape of catalyst. FIG. 5A showed tipgrowth mechanism for CNT structure formation, multi walls can be seeninside a tube in FIG. 5B, whereas catalyst particle is clear in FIG. 5Con which different layers of carbon are surrounding to make multi walls.

FIG. 6B-6C are details of energy-dispersive X-ray spectroscopy (EDS) ofsample area shown in FIG. 6A. Outer diameter of CNT varied between 15 nmto 39 nm. High aspect ratio (l/d) achieved from synthesized CNT rangingfrom 8,000-12,000 (FIG. 7A and FIG. 7B).

The crystallization and alignment of CNT increased when H₂ concentrationwas increased during the reaction. In the absence of Ar and totalreducing environment of H₂; large filament of CNT produced which showedvery high aspect ratio (FIG. 7B). The aligned and wafer form of CNT isformed due to layer by layer coverage of CNT bundles on each other, asshown in FIGS. 7A-7C. This is a very rare phenomenon in CVD reactor butby using wide range atomization nozzle in ultrasound atomization systemwe successfully produced various run of wafer form CNT. A wide rangeatomizer nozzle has not been reported previously for CNT production.

The invention claimed is:
 1. A hot-wall reactor method for makingferrocene-embedded multi-wall carbon nanotubes, comprising: atomizing aprecursor solution comprising xylene, ferrocene and a carrier gas,wherein the precursor solution is injected through an ultrasonicatomization system comprising an atomizing nozzle, a nozzle stem, and anultrasonic generating unit to form ultrasonic atomized precursordroplets; injecting the ultrasonic atomized precursor droplets from thetop of a vertical chemical vapor deposition reactor into a preheatingzone of the vertical chemical vapor deposition reactor; reacting areaction gas with the ultrasonic atomized precursor droplets in areaction zone of the vertical chemical vapor deposition reactor to forma film precursor that adsorbs to a growth surface in the verticalchemical vapor deposition reactor to form a layer of multi-wall carbonnanotubes comprising ferrocene particles embedded therein, wherein thereaction zone is heated with an electric furnace; and repeating theatomizing, the injecting of the ultrasonic atomized precursor molecule,and the reacting until one or more layers of the multi-wall carbonnanotubes are formed and then scraping the multi-wall carbon nanotubesfrom the growth surface of the vertical chemical vapor depositionreactor; wherein the multi-wall carbon nanotubes have an outer diameterof 10 nm-51 nm, a length to diameter aspect ratio of 7200-13200.
 2. Themethod of claim 1, wherein the carrier gas is argon.
 3. The method ofclaim 1, wherein the atomizing nozzle has a 0.1-0.2 cm aperture and aradial spray angle of 125°-140°.
 4. The method of claim 1, wherein thereaction zone is heated to a temperature of 750° C.-1100° C.
 5. Themethod of claim 1, wherein the reacting takes place at a pressure lessthan 1.5 bar and a constant temperature.